How many peels does a cat-stop need so the cat-stop will stop cats? :D

Janie, I focus on newly-planted ground and a 2 meter deep boundary line around the area about which I'm concerned. We are dealing with even more square feet than your nice yard, but the cats have fairly predictable routes in and out. Your cat population is concentrated, so you will likely need several approaches (some of which you've put into practice).

A combination of visual, scent, and physical barriers (including animal removal) has the strongest, longest lasting effect, as it does for deer and various other unwelcome animals.